Inlaids are made either by embedding three-dimensional chips into a clear plastisol matrix or by compacting (or sintering) three-dimensional chips into a solid patterned mass. It is with the former processing technique that this invention is concerned. U.S. Pat. No. 4,212,691 and Canadian Pat. No. 1,060,282 are typical of prior art processes.
When three-dimensional particles are embedded in what is usually a thin layer of plastisol, it is difficult to produce the resultant embedded matrix with a smooth and uniform surface. Such a surface may be required, for example, to facilitate further processing and finishing. In the past, the production of a smooth, uniform surface has involved subsequent coating to smooth the embedded plastisol matrix and, optionally, the use of a rotating drum with back-up roller to compress and smooth the embedded plastisol matrix, either before or after coating.
When a subsequent coating of the completely gelled particle embedded plastisol is employed to smooth surface roughness, there is a tendency for air to become trapped under the coating and form visible bubbles which blemish the final product. The bubble formation occurs at the coatings' interface and is believed to be directly attributable to the surface roughness of the embedded plastisol matrix.
Also, when the particles used have one dimension significantly different from the other two dimensions, eg. flat or needle shaped particles, it is difficult to reduce the thickness of the coating/particle layer to less than the maximum dimension of a single particle. This is because embedding and smoothing by the prior art compression techniques discussed above results in random orientation of the embedded particles.
Processes using the above discussed embedding approaches generally require several steps to embed, gel and smooth the surface of the particle embedded coating. For example, in Canadian Pat. No. 1,060,282 the chips are applied to the wet, ungelled plastisol, which is then partially gelled and, thereafter, passed between a heated drum and a back-up roll to complete gelling and to smooth the surface of the coating. This patent also teaches that, where a clear wear layer is used over the layer containing the chips, it is preferred, prior to application of the wear layer, to smooth the plastic layer containing the chips, as by pressing the solidified, gelled layer against a roll.
U.S. Pat. No. 4,212,691 discloses depositing a substantially uniform layer of decorative chips upon a moving and vibrating substrate coated with an ungelled plastisol having a wet, tacky surface. The chips are deposited from a rolling bank of chips formed at a seal blade in contact with the surface. This is followed by a consolidation procedure, whereby the chips and the ungelled layer are compressed into a single layer and the ungelled plastisol transformed into a gelled plastisol. The consolidation procedure employs a large, steam-heated, rotatable, cylindrical drum having a plurality of heated, rotatable, pressure-applying cylindrical press rolls capable of applying pressure to any material placed on the surface of the heated, cylindrical drum.
The subject invention, which utilizes a novel technique for embedding particles in a plastisol coating while simultaneously gelling the plastisol/particle matrix layer, provides an improved process for producing inlaids. The invention capitalizes on and overcomes the inherent disadvantages of prior art embedding processes, such as those discussed above, and improves upon them by providing a novel means for smoothing the particle embedded plastisol layer while it is still in the fluid state. This improved process is uniquely suited for large scale, commercial production of sheet vinyl flooring and wall covering of the inlaid type, as well as other decorative inlaid types of sheet materials, particularly of the resilient type.
The process of this invention offers the specific advantages of providing, in one step, an inlaid matrix of uniform thickness, gelled throughout, with a firm and smooth surface. At the same time the process permits a lower coating/particle layer thickness (relative to particle size), denser particle loading and significantly improved orientation of flat or needle shaped particles.